Drive control device of motor and a method of start-up

ABSTRACT

A drive control device of motor capable of starting up even a motor of such a type that the polarity of induced voltage does not switch every 180° of electrical angle or the polarity, positive or negative, does not occur with accuracy without causing a reverse rotation is provided. In a start-up control of motor, the following operation is performed: a current is passed through any coils in two phases, and the polarity of voltage induced in the non-conducting phase is detected. A conducting phase at start-up is determined based on the detected polarity of induced voltage. The average value of induced voltages in non-conducting phase detected with respect to the coils in respective phases is determined. The average value and the detected induced voltages are compared with each other, and relative polarities are determined from the magnitude relation with the average value to determine a conducting phase at start-up.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application of U.S. Ser. No. 11/248,305, filedOct. 13, 2005 now U.S. Pat. No. 7,411,365. The present applicationclaims priority from Japanese patent application No. 2004-299799 filedon Oct. 14, 2004, the content of which is hereby incorporated byreference into this application.

BACKGROUND OF THE INVENTION

The present invention relates to a drive control technology forbrushless motors and a technology effectively applicable to start-upcontrol on three-phase direct-current motors. More particularly, itrelates to a technology that can be effectively utilized for a drivecontrol device of a spindle motor that rotatably drives storage media ina desk-type storage device, such as a hard disk unit (hard disk driver).

To rotate a magnetic disk as storage media in a hard disk unit, abrushless three-phase direct-current motor designated as spindle motoris in general use. A magnetic disk is rotated at high speed by a spindlemotor, and a magnetic head for read/write is brought close to thesurface of the rotating magnetic disk and moved in the radial directionto write or read information.

The following method has be conventionally used in drive control on abrushless motor: the positional relation between rotor and stator isdetected using a Hall element; a coil phase with which energizationshould be started is determined from the detected positional relation toprevent the reverse rotation of the motor. However, sensorless motorshave been brought into greater use with respect to hard disk units. Thisis because, when a motor is provided with a rotor position detectorusing a Hall element, it is difficult to reduce the size of theequipment. Such sensorless motors have a problem. If the positionalrelation between rotor and stator is unknown when the rotation of amotor is started, the rotor can make a reverse rotation.

To cope with this, the present applicants proposed the following controlmethod: so short a pulse current that a rotor does not react is passedthrough any coils in two phase; the polarity of an induced voltage thatoccurs in the non-conducting phase is detected to determine thepositional relation between rotor and stator; the characteristic thatthe polarity of an induced voltage is switched every 180° of electricalangle is utilized to determine a phase with which energization should bestarted; the reverse rotation of this sensorless motor at start-up isthereby avoided. (Refer to Patent Document 1.)

[Patent Document 1] Japanese Unexamined Patent Publication No.2001-275387

[Patent Document 2] Japanese Unexamined Patent Publication No.2004-140975

SUMMARY OF THE INVENTION

Recently, various polyphase direct-current motors have been placed onthe market. In these polyphase direct-current motors, the methods ofrotor magnet magnetization, the shapes of cores, and the like are variedin order to suppress vibration, noise, and uneven rotation throughstructural devices. The present inventors applied the start-up controlmethod disclosed in Patent Document 1 to several polyphasedirect-current motors recently put on the market. This method is suchthat an energization start phase is determined from the polarity of aninduced voltage occurring in a non-conducting phase. As a result, thepresent inventors found that motors might make a reverse rotation, andinvestigated in an attempt to track down the cause.

The result of the investigation revealed the following: as illustratedin FIGS. 22B to 22D in Japanese Unexamined Patent Publication No.2004-140975, a number of motors changed the polarity of an inducedvoltage every 180° of electrical angle. As illustrated in FIGS. 22E to22G, however, some motors temporarily inverted the polarity of aninduced voltage in proximity to a zero cross point of back electromotiveforce. Application of the start-up control method disclosed in PatentDocument 1 to a motor could cause a reverse rotation. Consequently, thepresent inventors made an invention related to a method of start-up andfiled an application for this invention (Patent Document 2). With thismethod, even a motor of such a type that the polarity of an inducedvoltage is temporarily inverted in proximity to a zero cross point ofback electromotive force can be started up without causing a reverserotation.

However, the following fact thereafter came out: various types of motorshad been placed on the market in addition to such motors that thepolarity of an induced voltage is temporarily inverted in proximity to azero cross point of back electromotive force. Such motors include:motors of such a type that the polarity of an induced voltage does notswitch every 180° of electrical angle; and motors of such a type thatthe magnitude of an induced voltage is small and its polarity, positiveor negative, does not occur with accuracy.

An object of the present invention is to provide a rotary drive controldevice that is capable of starting a brushless polyphase direct-currentmotor without causing a reverse rotation even if the motor is of such atype that the polarity of an induced voltage does not switch every 180°of electrical angle or the polarity, positive or negative, does notoccur with accuracy.

The above and other objects and features of the present invention willbe apparent from the description of this specification and theaccompanying drawings.

The following is a brief description of the gist of the representativeelements of the invention laid open in this application.

That is, in start-up control on a motor, a current is passed through anycoils in two phases; the polarity of a voltage induced in thenon-conducting phase is detected; and a conducting phase at start-up isdetermined based on the detected polarity of induced voltage. Thisstart-up control is so constructed that the induced voltages ofnon-conducting phases detected with respect to coils in various phasesare averaged; the detected induced voltages are compared with theaverage value; and the relative polarity of each induced voltage isdetermined based on its magnitude relation with the average value todetermine a conducting phase at start-up.

All the curves obtained by plotting the induced voltages of coils inrespective phases cross a line indicating the average value of theinduced voltages of the coils in all the phases without exception.Therefore, the following advantage is brought by comparing the averagevalue of the induced voltages of coils in respective phases withdetected induced voltages, and thereby identifying relative polaritiesto determine a conducting phase at start-up, as by the above-mentionedmeans: even a motor of such a peculiar type that the polarity of aninduced voltage does not switch every 180° of electrical angle or thepolarity, positive or negative, does not occur with accuracy can bereliably started up without causing a reverse rotation.

The following is a brief description of the gist of effects obtained bythe representative elements of the invention laid open in thisapplication.

According to the present invention, even a brushless polyphasedirect-current motor of such a peculiar type that the polarity of aninduced voltage does not switch every 180° of electrical angle or thepolarity, positive or negative, does not occur with accuracy can bereliably started without causing a reverse rotation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuitry diagram illustrating the general configuration ofthe drive control circuit in a three-phase direct-current motor to whichthe present invention is effectively applicable.

FIGS. 2A and 2B are explanatory drawings illustrating an energizingmethod for detecting the position of a rotor in a drive control circuitin an embodiment and a detecting method for the induced voltage in anon-conducting phase.

FIG. 3 is a waveform chart illustrating the phase relation betweenvoltages induced in a non-conducting phase and back electromotive forcesin a commonly used three-phase direct-current motor.

FIG. 4 is a waveform chart illustrating the phase relation between thepolarities of induced voltages and back electromotive forces in acommonly used three-phase direct-current motor.

FIG. 5 is a waveform chart illustrating the phase relation betweenvoltages induced in a non-conducting phase and back electromotive forcesin a peculiar three-phase direct-current motor.

FIG. 6 is a waveform chart illustrating the phase relation between thepolarities of induced voltages and back electromotive forces in apeculiar three-phase direct-current motor.

FIG. 7 is a waveform chart illustrating the phase relation between thepolarities and the magnitude of levels of induced voltages and backelectromotive forces in a peculiar three-phase direct-current motor.

FIG. 8 is a waveform chart illustrating the relation between inducedvoltages and the average value of induced voltages in three phases insuch a three-phase direct-current motor that the induced voltage in anyphase has an offset.

FIG. 9 is a waveform chart illustrating the relation between inducedvoltages and the average value of induced voltages in three phases insuch a three-phase direct-current motor that variation in inducedvoltage contains dents.

FIG. 10 is a block diagram illustrating an example of the configurationof the polarity detection unit of a motor drive control circuit in anembodiment.

FIG. 11 is a block diagram illustrating an example of the configurationof the output current control unit of a motor drive control circuit inan embodiment.

FIG. 12 is a flowchart illustrating an example of a start-up controlprocedure using a sequencer in a motor drive control circuit in anembodiment.

FIG. 13 is a time diagram illustrating the operation timing for start-upcontrol in a motor drive control circuit in an embodiment.

FIG. 14 is a block diagram illustrating an example of the configurationof the polarity detection unit of a motor drive control circuit in asecond embodiment.

FIG. 15 is a flowchart illustrating an example of a start-up controlprocedure using a sequencer in a motor drive control circuit in a secondembodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, description will be given to preferred embodiments of thepresent invention with reference to the drawings.

FIG. 1 illustrates the general configuration of the drive controlcircuit in a three-phase brushless direct-current motor.

In FIG. 1, reference marks Lu, Lv, and Lw denote the stator coils inthree phases, phase U, phase V, and phase W, respectively, of a motorMT; and reference marks B-emf(U), B-emf(V), and B-emf(W) denote the backelectromotive forces of the coils Lu, Lv, and Lw in the respectivephases as voltage sources. Numeral 110 denotes an output driver circuitfor applying voltage to the terminal of each coil and passing a drivingcurrent through it. Reference marks M1 to M3 denote high potential-sideoutput transistors that cause a current to flow into the coils inrespective phases. Reference marks M4 to M6 denote low potential-sideoutput transistors that pull a current from the coils in respectivephases. Numerals 111 to 113 denote pre-drivers that apply gate voltageto the output transistors M1 to M6 to control driving currents for thecoils. The source terminals of the above low potential-side outputtransistors M4 to M6 are connected in common and connected to a groundpotential point through a current sense resistor Rsns. The drive controlcircuit is so constructed that a direct current flowing from a powersource to a ground point through the motor coils is caused to flow tothe sense resistor Rsns.

Numeral 120 denotes an output current control unit that generates PWMsignals for controlling output currents and supplies them to the outputdriver circuit 110. A voltage corresponding to a direct current detectedby the current sense resistor Rsns is fed back to this output currentcontrol unit 120. The output current control unit generates and outputspulse signals UPWM, VPWM, and WPWM for PWM control on the output drivercircuit 110 so that the detected output current agrees with a currentcommand value supplied from a controller, not shown.

Numeral 130 denotes an induced voltage detection unit that detects aninduced voltage induced in the coil in a non-conducting phase incorrespondence with the currents passed through any coils in two phases.This induced voltage detection unit 130 comprises: a selection circuit131 comprised of three switches for selecting a coil whose inducedvoltage is to be detected; a differential amplifier 132 that amplifiesthe potential difference between one terminal voltage of the coilselected by the selection circuit 131 and the voltage at a center tap CTto which one ends of the coils are connected in common and outputs it; afilter 133 that cuts noise contained in the output of the differentialamplifier 132; and an A-D converter circuit 134 that converts the outputvoltage of the differential amplifier 132 into a digital signal byA-to-D conversion.

Numeral 140 denotes a polarity detection unit. The polarity detectionunit determines the polarity of an induced voltage detected by theinduced voltage detection unit 130. In addition, it determines theaverage value of the induced voltages in non-conducting phase detectedwith respect to the coils in respective phases. Then the polaritydetection unit compares the average value with a detected inducedvoltage and determines a relative polarity based on the magnituderelation with the average value. Numeral 150 denotes a decoder unit thatdecodes the output of the polarity detection unit 140 to determine aphase in which a current is to be passed and supplies the output currentcontrol unit 120 with a signal indicating the conducting phase. Numeral160 denotes a sequencer that controls the entire drive control circuitin FIG. 1 in accordance with a predetermined control procedure inresponse to an input command. The sequencer 160 is supplied with signalsindicating a determined conducting phase from the decoder unit 150, andgenerates and outputs signals for controlling each part according tothese signals.

Description will be given to how a conducting phase at start-up of amotor is determined in a drive control circuit in this embodiment.

In this embodiment, for example, the following operation is performed:as illustrated in FIG. 2A, so minute an electric current that a rotordoes not react is caused to flow from a phase V coil Lv to a phase Wcoil Lw. The induced voltage Vm+ induced in a phase U coil Lu at thistime is detected. As illustrated in FIG. 2B, subsequently, a current iscaused to flow from the phase W coil Lw to the phase V coil Lv. Theinduced voltage Vm− induced in the coil Lu in phase U, thenon-conducting phase, at this time is detected. The sum of the inducedvoltages is worked out, and the obtained value is stored in a registeror the like.

Next, a current is caused to flow from the phase U coil Lu to the phaseV coil Lv, and the induced voltage Vm+ induced in the phase W coil Lw atthis time is detected. Subsequently, a current is caused to flow fromthe phase V coil Lv to the phase U coil Lu, and the induced voltage Vm−induced in the phase W coil Lw at this time is detected. The sum of theinduced voltages is worked out, and the obtained value is stored in aregister or the like. Further, a current is caused to flow from thephase W coil Lw to the phase U coil Lu, and the induced voltage Vm+induced in the phase V coil Lv at this time is detected. Subsequently, acurrent is caused to flow from the phase U coil Lu to the phase W coilLw, and the induced voltage Vm− induced in the phase V coil Lv isdetected. The sum of the induced voltages is worked out, and theobtained value is added to the already detected detection valuesassociated with the phase U coil Lu and the phase W coil Lw to determinea value equivalent to the average value. (This value is a value threetimes the average value in this embodiment.) Thereafter, this valueequivalent to the average value is compared with the detected inducedvoltages in respective phases. (The detected induced voltages takevalues obtained by tripling the detection values in this embodiment.)Thus, relative polarities are identified, and a conducting phase atstart-up is determined.

As illustrated in FIG. 3, the waveform B of the non-conducting phaseinduced voltage of a common three-phase direct-current motor presentlyon the market is advance in phase from the waveform A of backelectromotive force by approximately 90° of electrical angle. To startup a motor whose induced voltage has such characteristics as illustratedin FIG. 3, such a procedure as illustrated in FIG. 4 is taken. Thepolarities of induced voltages in respective phases are detected. Whenthe polarities of induced voltages in phases U, V, and W are “negative,”“negative,” and “positive,” the conducting phase is determined as phaseV→phase U. When the polarities of induced voltages in phases U, V, and Ware “positive,” “negative,” and “positive,” the conducting phase isdetermined as phase W→phase U. When the polarities of induced voltagesin phases U, V, and W are “positive,” “negative,” and “negative,” theconducting phase is determined as phase W→phase V. When the polaritiesof induced voltages in phases U, V, and W are “positive,” “positive,”and “negative,” the conducting phase is determined as phase U→phase V.When the polarities of induced voltages in phases U, V, and W are“negative,” “positive,” and “negative,” the conducting phase isdetermined as phase U→phase W. When the polarities of induced voltagesin phases U, V, and W are “negative,” “positive,” and “positive,” theconducting phase is determined as phase V→phase W. The motor can bestarted up by controlling the output driver circuit so as to pass acurrent in accordance with this determination. This method of start-upis the method of start-up disclosed in Japanese Unexamined PatentPublication No. 2001-275387.

Recently, various three-phase direct-current motors have come on themarket to reduce noise and vibration. It was found that some of thesemotors had an offset like the characteristic line B′ obtained byplotting hollow circles, shown in FIG. 5, depending on the method ofrotor magnet magnetization, the shape of core, or the like. Further, itwas found that such motors did not switch the polarity of inducedvoltage to negative (or positive). The table shown at the lower part ofFIG. 6 illustrates the polarities of the induced voltages of the coilsin respective phases of a motor having such a characteristic. Unlike inthe table shown in FIG. 4, all the cells for polarity in phase Uindicate “positive” in the table in FIG. 6. It can be seen that, in somecases, a motor cannot be rotated in a proper direction with the methodof start-up disclosed in Japanese Unexamined Patent Publication No.2001-275387 in which a conducting phase and an energizing direction aredetermined based on the result of determination of polarity, positive ornegative.

The start-up control in this embodiment is so constructed that thefollowing is implemented: the average value of detected induced voltagesis worked out, and the average value is compared with the detectedinduced voltages to determine relative polarities; and a conductingphase and an energizing direction are determined from the result of thedetermination. Thus, even a motor whose induced voltage has such acharacteristic (offset) as illustrated in FIG. 5 can be started upwithout fail. In FIG. 3 and FIG. 5, the normalized voltage representedon the vertical axis is a voltage obtained by converting the maximumvalue of an induced voltage into 1V and the minimum value into −1V. FIG.5 illustrates a case where only the induced voltage in phase U has anoffset. There are cases where an induced voltage in any other phase, orinduced voltages in two phases of the three phases or in all the threephases have an offset. In these cases as well, the start-up control inthis embodiment is effective.

FIG. 7 illustrates the following in a case where this embodiment isapplied to the drive control circuit of a motor whose induced voltagehas an offset: the relation between the phases of back electromotiveforces and the timing of change in induced voltages; and the relationbetween the result of determination of the relative polarities ofinduced voltages, conducting phases, and the phases in which the nextdetection is to be carried out. As is apparent from the waveform in FIG.7, the absolute polarity of induced voltage in phase U is constantly“positive.” As illustrated in the table at the lower part of FIG. 7, therelative polarity is “negative” between electrical angles of −180° and−120° and between electrical angles of +60° and +180°. The comparison ofthe table at the lower part of FIG. 7 and the table shown in FIG. 4reveals the following: both are identical with each other, and aconducting phase can be properly determined by applying this embodimenteven if the polarity of induced voltage is not inverted between positiveand negative.

FIG. 8 indicates the relation between change in induced voltages inphases U, V, and W and values (solid diamonds) obtained by averagingthem in a motor in which the induced voltage in any phase (e.g., phaseU) has an offset. FIG. 9 indicates the relation between change ininduced voltages in phases U, V, and W and values (solid diamonds)obtained by averaging them in a motor in which induced voltages containdents and on which Japanese Unexamined Patent Publication No.2004-140975 focuses attention. The waveforms in FIG. 8 and FIG. 9 revealthe following: all the curves obtained by plotting induced voltages ofcoils in respective phases cross a line indicating the average value ofthe induced voltages of the coils in all the phases without exception;therefore, the following advantage is brought by comparing the averagevalue of the induced voltages of coils in respective phases withdetected induced voltages, and thereby identifying relative polaritiesto determine a conducting phase at start-up: even a motor of such apeculiar type that the polarity of an induced voltage does not switchevery 180° of electrical angle or the polarity, positive or negative,does not occur with accuracy can be reliably started up without causinga reverse rotation.

The drive control circuit in this embodiment is so constructed that theabove-mentioned identification of the relative polarities of inducedvoltages and determination of a conducting phase based on the result ofthe determination are carried out by the polarity detection unit 140,decoder 150, and sequencer 160. Hereafter, description will be given tothe configuration and operation of the polarity detection unit 140 andthe output current control unit 120 with reference to FIG. 10 and FIG.11. Description will also be given to a start-up control procedure usingthe sequencer 160 with reference to the flowchart in FIG. 12.

FIG. 10 illustrates an example of the configuration of the polaritydetection unit 140. The polarity detection unit 140 in this embodimentcomprises: an integrator 141 that cumulatively adds induced voltagevalues detected by the induced voltage detection unit 130 anddigitalized by the A-D converter 134; registers 142 a and 142 b thatstore voltages in two phases (e.g., phase U and phase V) of detectedinduced voltages; an adder 143 b that adds together a value stored inthe register 142 b and an induced voltage (phase W) detected at theintegrator 141; an adder 143 a that adds together a value stored in theregister 142 a and a value computed by the adder 143 b; a selector 144that selects any one from among the values stored in the registers 142 aand 142 b and an induced voltage detected at the integrator 141; amultiplier 145 that triples the selected value; and a subtracter 146that computes the difference between the result of computation by themultiplier 145 and the result of computation by the adder 143 a.

In addition, the polarity detection unit 140 comprises: a comparator 147for polarity determination that compares the output value of thesubtracter 146 with a reference value (ground potential) and therebydetermine a relative polarity; polarity registers 148 a/148 b, and 148 cthat respectively store the results of determination by the comparator147; and a selector 149 that allows the results of determination by thecomparator 147 to be transmitted to the corresponding polarity registers148 a, 148 b, and 148 c and stored there. Each of the selectors 144 and149 is so constructed that any one correcting switch is turned onaccording to a selection signal SEL1, SEL2, or SEL3, and the tworemaining switches are kept off.

The registers 142 a and 142 b respectively take in signals USENS andVSENS indicating the detection timing for phase U and phase V, suppliedfrom the sequencer 160, and hold them. The integrator 141 comprises anadder ADD and a register REG. A value in the register REG is fed back tothe adder ADD, and is added to an input value in synchronization withclock CLK. The integrator thereby carries out cumulative addition. Insynchronization with signals USENS, VSENS, and WSENS indicating thedetection timing for phase U, phase V, and phase W, respectively, theregister REG holds the cumulative value at that time for a predeterminedtime. The polarity registers 148 a, 148 b, and 148 c perform latchoperation according to signals LAT1 to LAT3 indicating latch timingsupplied from the sequencer 160.

The selector 149 is controlled according to selection signals SEL1 toSEL3 supplied from the sequencer 160. The results for phases determinedby the comparator 147 are stored in the corresponding polarity registers148 a to 148 c. They are outputted as signals Upole, Vpole, and Wpoleindicating the polarities of induced voltages in respective phases fromthe polarity registers 148 a to 148 c to the decoder unit 150.

The decoder unit 150 decodes the signals Upole, Vpole, and Wpoleindicating polarities from the polarity detection unit 140. Then itgenerates signals UPON, UNON, VPON, VNON, WPON, and WNON for driving andcontrolling the coils in respective phases in accordance with theenergizing directions shown on the second line from bottom in the tablein FIG. 7, and outputs them. At the same time, the decoder unitgenerates a selection signal SEL0 that informs the sequencer 160 of thedetermined conducting phase, and outputs it to the sequencer. Thus, notonly a motor of such a peculiar type that the polarity of inducedvoltage does not switch every 180° of electrical angle or the polarity,positive or negative, does not occur with accuracy can be properlystarted up. But also a common motor in which the polarity switchesbetween positive and negative can be properly started up.

The signals UPON, VPON, WPON, UNON, VNON, and WNON outputted from thedecoder unit 150 mean the following: when the signals UPON, VPON, andWPON are at high level, voltage Vspn is applied to the coil terminal inthe corresponding phase to cause a current to flow in; when the signalsUNON, VNON, and WNON are at high level, the coil terminal in thecorresponding phase is connected to a ground point to pull in a current;when both the signals UPON, VPON, and WPON and the signals UNON, VNON,and WNON are at low level, the coil terminal in the corresponding phaseis set to a high impedance, that is, it is brought into a non-conductingphase.

As illustrated in FIG. 11, the output current control unit 120comprises: a subtracter 121 that computes the difference between ISENSEobtained by converting a voltage in proportion to a coil currentdetected by the sense resistor Rsns during steady-state rotation controlinto a digital value at the A-D converter 134 and a current commandvalue supplied from a controller, not shown; a filter 122 for preventingoscillation in a current control system; a pulse generation circuit 123that generates a PWM pulse of a predetermined frequency having a pulsewidth corresponding to the output voltage of the filter 122; a PWMmodulation circuit 124; and the like. The PWM modulation circuitgenerates and outputs the following signals according to theenergization control signals UPON and UNON; VPON and VNON; and WPON andWNON from the decoder unit 150 and the timing signals USENS, VSENS, andWSENS from the sequencer 160: a PWM driving signal UPWM for a phase Upre-driver 111 or a signal UHIZ giving an instruction to set the phase Uterminal to a high impedance; a PWM driving signal VPWM for a phase Vpre-driver 112 or a signal VHIZ giving an instruction to set the phase Vterminal to a high impedance; and a PWM driving signal WPWM for a phaseW pre-driver 113 or a signal WHIZ giving an instruction to set the phaseW terminal to a high impedance.

When a motor is started up, the output current control unit 120generates the following signals and supplies them to the pre-drivers111, 112, and 113 according to a signal from the PWM modulation circuit124: a driving signal for carrying out energization for induced voltagedetection for a predetermined time and a PWM modulating signal obtainedby carrying out such PWM drive control that a current passed through thesense resistor Rsns is matched with a current command value from thecontroller. These signals are alternately switched from the USENS,VSENS, and WSENS signals. The output current control unit is soconstructed that the following is implemented: when the number of motorrotations reaches a predetermined value, the acceleration of the motorby induced voltage detection is terminated; only such PWM drive controlmentioned above that the current passed through the sense resistor Rsnsis matched with a current command value from the controller is therebycarried out. The A-D converter 134 is used in common to convert avoltage detected by the induced voltage detection unit 130 and a coilcurrent detected by the sense resistor Rsns into digital signals.

Description will be given to the start-up control procedure using thesequencer 160 with respect to the flowchart in FIG. 12. FIG. 13 is atiming diagram of this start-up control.

When start-up control is started, the sequencer 160 resets the registerREG of the integrator 141 for cumulatively holding the results of A-Dconversion, provided in the polarity detection unit 140 illustrated inFIG. 10 (Step S1). Thereafter, a current of such a short pulse that therotor does not react is caused to flow from the coil in phase V to thecoil in phase W. The induced voltage that occurs in the coil in “phaseU” due to the phenomenon of mutual induction at that time is detected bya predetermined number of times. The results obtained by converting thedetected induced voltages through the A-D converter circuit 134 arecumulated in the integration register 141. The direction of the currentis inverted, and the same operation is repeated. The polarity and levelof the induced voltage in phase U are determined based on the values inthe integration register, and the result of the determination is latchedinto the register 142 a (Step S2).

The register of the integrator 141 is reset again, and then a current ofsuch a short pulse that the rotor does not react is caused to flow fromthe coil in phase U to the coil in phase W. This time, the inducedvoltage that occurs in the coil in “phase V” is detected by apredetermined number of times. The results obtained by converting thedetected induced voltages through the A-D converter circuit 134 arecumulated in the register of the integrator 141. The direction of thecurrent is inverted, and the same operation is repeated. The polarityand level of the induced voltage in phase V are determined based on thevalues in the integration register, and the result of the determinationis latched into the register 142 b (Steps S3 and S4.)

Thereafter, the register of the integrator 141 is reset once again, andthen a current of such a short pulse that a rotor does not react iscaused to flow from the coil in phase U to the coil in phase V. Thistime, the induced voltage that occurs in the coil in “phase W” isdetected by a predetermined number of times. The results obtained byconverting the detected induced voltages through the A-D convertercircuit 134 are cumulated in the register of the integrator 141. Thedirection of the current is inverted, and the same operation isrepeated. The polarity and level of the induced voltage in phase W aredetermined based on the values in the integration register (Steps S5 andS6), and the result of the determination is held in the register REG ofthe integrator 141.

Subsequently, the selector 144 is controlled to transmit the values inthe registers 142 a, 142 b, and REG to the multiplier 145 one by one.Each detection value is tripled there, and the result obtained by addingthe values in the registers REG, 142 b, and 142 a at the adders 143 aand 143 b is subtracted from it. The subtraction value is compared withthe reference value at the comparator 147 to determine the relativepolarity of induced voltage in each phase. Further, the selector 149 iscontrolled to latch the results of polarity determination into thecorresponding registers 148 a/148 b, and 148 c (Steps S7 to S9).Thereafter, these results of polarity determination are transmitted tothe decoder unit 150 to determine a conducting phase (the direction ofenergization) (Step S10).

Subsequently, the operation proceeds to Step S11, and the value on acounter is referred to determine whether a predetermined number of timesof energization of the coils have been completed or not. If they havenot been completed yet, energization is carried out in the conductingphase determined at Step S10 for a predetermined relatively short time,and the energization counter is incremented (Step S12). Then, theintegration register REG is reset (Step S13), and a current of such ashort pulse that the rotor does not react is passed between the coil inphase v and the coil in phase W. The induced voltage that occurs in thecoil in “phase U” due to the phenomenon of mutual induction at that timeis detected (Step S14). Similarly, the integration register REG isreset, and then a current is passed between the coil in phase W and thecoil in phase U. The induced voltage that occurs in the coil in “phaseV” due to the phenomenon of mutual induction at that time is detected;and a current is passed between the coil in phase U and the coil inphase V, and the induced voltage that occurs in the coil in “phase W”due to the phenomenon of mutual induction at that time is detected(Steps S15 to S18). At this time, the sequencer 160 generates aselection signal SEL1, SEL2, or SEL3 corresponding a signal SEL0indicating the sense phase in which the induced voltage should bedetected next, based on the signal SEL0, and outputs it. The signal SEL0is supplied from the decoder unit 150 based on the result of polaritydetermination.

Based on the results of detection at Steps S2 to S6, a phase in whichthe polarity should be determined at the decoder unit 150. The selector144 is controlled in accordance with this determination, and withrespect to the determined phase, computation is carried out by thecomputing units 143 a, 143 b, 145, and 146 shown in FIG. 10. Using theresult of the computation, it is determined at the comparator 147whether the relative polarity of the induced voltage in that phase ispositive or negative (Steps S19 and S20). The reason why the polarity isdetermined with respect to only one phase is as follows: as is apparentfrom the table at the lower part of FIG. 7, once energization is carriedout in a determined phase, the phase in which the polarity changes nextis uniquely determined. Therefore, unlike before the start ofenergization, a conducting phase can be determined only by polaritycomputation and determination in one phase after energization is carriedout.

Based on the result of determination at Step S20, the phase anddirection in which energization should be carried out next aredetermined at the decoder unit 150 (Step S21). Then the operationreturns to Step S11, and the above-mentioned procedure is repeated.Thus, the rotational speed of the rotor is gradually increased. If it isdetermined at Step S11 that a predetermined number of times ofenergization have been completed, the start-up control process isterminated, and the operation transitions to feedback control based on acurrent command value from the controller.

If the result of determination of the polarity of induced voltagecarried out at Step S20 is the same as the previous result, the samephase (e.g., phase U) as the previous time is selected as sense phase atStep S21. Then, energization is carried out in the same phase (e.g.,phase U→phase V). If the result of determination carried out at Step S20differs from that at the previous time, the phase (e.g., phase W)expected next is selected as sense phase at Step S19, and energizationis carried out in the corresponding phase (e.g., phase U→phase W) atStep S21. Thus, once energization is started, a conducting phase isdetermined only by polarity determination in one phase. This brings thefollowing advantages: the time required for determining a conductingphase can be shortened as compared with cases where polaritydetermination is carried out with respect to all the three phases, andthe conducting phase can be changed in the direction of normal directionwithout fail.

FIG. 14 and FIG. 15 illustrate another example of a motor drive controlcircuit according to the present invention.

The drive control circuit in this embodiment is substantially the sameas the drive control circuit in the first embodiment. One differencefrom the first embodiment is as follows: a register 142 c and an ANDgate G0 are provided in the stage subsequent to the registers 142 a and142 b that store induced voltages detected at the polarity detectionunit 140, illustrated in FIG. 10. The register 142 c stores valuesobtained by adding together all the induced voltages detected withrespect to coils in three phases, that is, a value equivalent to theaverage value of induced voltages in three phases. The AND gategenerates a signal providing the latch timing therefor. Anotherdifference is as follows: the start-up control on a motor is simplifiedin correspondence with the foregoing.

More specific description will be given. Provision of the register 142 cthat stores the value equivalent to the average value of inducedvoltages in three phases makes unnecessary the detection of inducedvoltages in three phases at Steps S13 to S18 in the control flowchart inFIG. 12. Thus, the induced voltage only in one phase is detected andpolarity determination is carried out based thereon. For this reason,the control flow in this embodiment is implemented as illustrated inFIG. 15. That is, after energization at Step S12, a phase in whichpolarity determination should be carried out is determined at thedecoder unit 150 based on the results of detection at Steps S2 to S6(Step S13′). Induced voltage is detected with respect only to thedetermined phase (Steps S14′ and S15′), and polarity determination iscarried out based on this detection to determine a conducting phase(Steps S16′ and S17′).

In this embodiment, as mentioned above, the induced voltage in one phaseonly has to be detected to determine a conducting phase, and thefollowing advantage is brought: the time required to start up a motor isshortened as compared with cases where the first embodiment is applied.The second embodiment is effectively applicable to start-up control on amotor of such a type that the average value of induced voltages does notvary so much as illustrated in FIG. 8. The reason for this is asfollows: when this embodiment is applied to start-up control on a motorof such a type that the average value of induced voltages greatly variesas illustrated in FIG. 9, the average value is varied according to adifference in the position of the rotor in a stop. This makes itdifficult to determine a polarity with accuracy.

Up to this point, specific description has been given to the inventionmade by the present inventors based on embodiments thereof. However, thepresent invention is not limited to the above-mentioned embodiments, andvarious medications can be made without departing from the spiritthereof, needless to add. Some examples will be taken. In thedescription of the motor drive control circuit in the above embodiments,a circuit that drives and controls a three-phase direct-current motor istaken as an example. The present invention is applicable to a polyphasedirect-current motor other than three-phase motors.

With respect to the embodiments, description has been given to start-upcontrol on a motor of such a peculiar type that the polarity of inducedvoltage does not switch every 180° of electrical angle or the polarity,positive or negative, does not occur with accuracy. The start-up controlcircuit in the above embodiments is also applicable to start-up controlon a common motor in which the polarity of induced voltage switchesevery 180° of electrical angle.

In the above embodiments, instead of working out the average value ofinduced voltages in three phases, values obtained by tripling the totalof values in three phases and the detection value in any phase at themultiplier are used to determine a relative polarity. Instead of amultiplier, a divider that works out the average value of inducedvoltages in three phases may be used. The above embodiments are providedwith two adders 143 a and 143 b that add together induced voltages inrespective phases to determine the value equivalent to the average valueof induced voltages in three phases. For example, the construction inFIG. 14 may be modified as follows: a selector is provided on the inputside of the adder 143 a so that the input value can be switched; and apath for returning the value in the register 142 c to the adder 143 a isprovided and the adder 143 b is thereby omitted.

The above description has been given mainly to cases where the inventionmade by the present inventors is applied to the drive control device ofa spindle motor for hard disk unit that is the field of utilizationunderlying the invention. The present invention is not limited to thisfield, but it can be utilized in a wide range of motor drive controldevices for driving brushless motors, including, for example, a motorthat rotates the polygon mirror of a laser beam printer and an axialflow fan motor.

1. A drive control device of a poly-phase direct current motor,comprising: an induced voltage detecting unit that detects an inducedvoltage of coils of a stator of the poly-phase direct current motorwherein when such a current that a rotor of the poly-phase directcurrent motor does not react is passed through any two phase coils ofthe poly-phase direct current motor in succession, the induced voltagedetecting unit detects the voltage induced in a non-conducting phase;and a polarity detection unit that determines a polarity of the inducedvoltage detected by the induced voltage detection unit and thatdetermines the average value of the induced voltages in thenon-conducting phases, wherein a value equivalent to an average value ofinduced voltages in all phases of the poly-phase direct current motor isdetermined and a polarity of induced voltage in each phase of thepoly-phase direct current motor is determined by comparison of thedetected induced voltages of the respective phases with the valueequivalent to the average value, and wherein a phase coil of thepoly-phase direct current motor through which a current should be passedto rotate the rotor and the direction of energization are determinedbased on results of the detection of induced voltages and the determinedpolarity in respective phases of the poly-phase direct current motor forrotating and starting-up of the rotor of the poly-phase direct currentmotor.
 2. The drive control device of a poly-phase direct current motoraccording to claim 1, further comprising: a three phase direct currentmotor as said poly-phase direct current motor having first, second andthird phase coils; a first holding circuit that holds a detection valueof the induced voltage occurring in the coil of the third phase as thenon-conducting phase when said current is passed through the coils ofthe first phase and second phase; a second holding circuit that holds adetection value of induced voltage occurring in the coil of the secondphase as the non-conducting phase when said current is passed throughthe coils of the first phase and third phase; and a third holdingcircuit that holds a detection value of induced voltage that occurs inthe coil of the first phase as the non-conducting phase when saidcurrent is passed through the coils in the second phase and the thirdphase, wherein the polarity detection unit determines the average valueof induced voltages in the non-conducting phases from the inducedvoltages held in the first, second and third holding circuits that isused by a polarity determination circuit in determining a plurality ofinduced voltages in each phase of the three phase direct current motor.3. The drive control device of motor according to claim 2, wherein acurrent having such an amplitude and a duration that the rotor reacts ispassed in accordance with the phase coil of the three-phasedirect-current motor and the direction of energization determined basedon results of determination by the polarity determination circuit,thereafter the induced voltages in all three phases of the three-phasedirect-current motor are detected again to determine again the valueequivalent to the average value thereof, the polarity of induced voltagein any phase of the three-phase direct-current motor is determined fromthe value equivalent to the average value determined again and theinduced voltage in a predetermined phase of the three-phasedirect-current motor, and the phase coil of the three-phasedirect-current motor through which a current should be passed and thedirection of energization are thereby determined.
 4. The drive controldevice of motor according to claim 2, comprising: a fourth holdingcircuit that holds the value equivalent to the average value, wherein acurrent having such an amplitude and a duration that the rotor of thethree-phase direct-current motor reacts is passed in accordance with thephase coil of the three-phase direct-current motor and the direction ofenergization determined based on result of determination by the polaritydetermination circuit, thereafter the induced voltage in a predeterminedphase of the three-phase direct-current motor is detected, the polarityof induced voltage in any phase of the three-phase direct-current motoris determined from the detected induced voltage and the value equivalentto the average value held in the fourth holding circuit, and a phasecoil of the three-phase direct-current motor through which a currentshould be passed and the direction of energization are therebydetermined.
 5. The drive control device of motor according to claim 2,wherein any one holding circuit of the first, second, and third holdingcircuits is provided in an accumulation circuit that accumulatesdetection values of induced voltages that occur in non-conducting phasewhen a current is passed through the two phase coils other than innon-conducting phase of the three-phase direct-current motor by a presetnumber of times, and is used to hold cumulative values when the inducedvoltages in all phases of the three-phase direct-current motor aredetected.